In the Processes for the Separation of gaseous mixtures by Adsorption (PSA), a large number of installation architectures and implementation cycles have been proposed.
For the production of oxygen from air, only, the number of adsorbers ranges from 1 to more than 4 and the adsorbent materials are selected from an extensive range. The variants of the cycles are particularly numerous.
The multiplication and coexistence of all these processes and architectures may be explained by taking into account the various financial parameters influencing the production costs for the gas or gases to be separated over production capacity intervals (which may vary over a range, the extremes of which have a ratio of 1 to 200), energy costs (which may vary by a factor of 1 to 6, depending on the country and purchasing conditions) and, lastly, the capital expenditures on the installations themselves.
Thus, between a large unit in a country where energy is expensive and a small unit in a country where energy is cheap, the cost of the electricity consumed, expressed relative to the production cost may vary, in the specific case of oxygen, from over 70% to less than 10%. It ensues that a given process and/or a given installation architecture will never be optimal over the entire range of potential custom. The tendency is therefore to select the process and/or architecture most suitable for a customer and/or a precise use in an `on-request` approach. Such an approach is already not very economical for relatively large units, but becomes prohibitive for small units or low-capacity units when the capital expenditure becomes preponderant and of considerable magnitude in absolute terms.
There is therefore a need to offer standard processes and installations that may nonetheless be adapted, particularly to local energy costs, in order to approach the optimal conditions usually achieved by the implementation of `tailor-made` processes and installations, particularly for the range of medium-capacity units which typically produce less than 30 or 40 tons of oxygen per day.